Thread overview  


October 12, 2009 Specializing on Compile Time Constants  

 
I'm working on a mathematical expression interpreter for D, which would allow for closed form mathematical expressions to be specified as string literals at runtime and be evaluated. For example: MathExp myExpression = mathExp("x^2 + e^cos(x)  2 * sqrt(pi)", "x"); writeln(myExpression(2)); // Does exactly what you think it does. I've found the syntax so convenient that I'd like to transparently specialize it on strings known at compile time. The idea is that, when the expression is hardcoded, you will still be able to use the MathExp interface, but your expression will evaluate at the full speed of a statically compiled function. Is there any way to test whether the value of an argument to a template function is known at compile time and specialize on this? 
October 12, 2009 Re: Specializing on Compile Time Constants  

 
Posted in reply to dsimcha  On 10/12/09 23:49, dsimcha wrote:
> I'm working on a mathematical expression interpreter for D, which would allow
> for closed form mathematical expressions to be specified as string literals at
> runtime and be evaluated. For example:
>
> MathExp myExpression = mathExp("x^2 + e^cos(x)  2 * sqrt(pi)", "x");
> writeln(myExpression(2)); // Does exactly what you think it does.
>
> I've found the syntax so convenient that I'd like to transparently specialize
> it on strings known at compile time. The idea is that, when the expression is
> hardcoded, you will still be able to use the MathExp interface, but your
> expression will evaluate at the full speed of a statically compiled function.
> Is there any way to test whether the value of an argument to a template
> function is known at compile time and specialize on this?
Doesn't all values to a template have to be known at compile time

October 12, 2009 Re: Specializing on Compile Time Constants  

 
Posted in reply to Jacob Carlborg  == Quote from Jacob Carlborg (doob@me.com)'s article
> On 10/12/09 23:49, dsimcha wrote:
> > I'm working on a mathematical expression interpreter for D, which would allow for closed form mathematical expressions to be specified as string literals at runtime and be evaluated. For example:
> >
> > MathExp myExpression = mathExp("x^2 + e^cos(x)  2 * sqrt(pi)", "x");
> > writeln(myExpression(2)); // Does exactly what you think it does.
> >
> > I've found the syntax so convenient that I'd like to transparently specialize
> > it on strings known at compile time. The idea is that, when the expression is
> > hardcoded, you will still be able to use the MathExp interface, but your
> > expression will evaluate at the full speed of a statically compiled function.
> > Is there any way to test whether the value of an argument to a template
> > function is known at compile time and specialize on this?
> Doesn't all values to a template have to be known at compile time
No, I mean the *function* parameters of a template function.

October 12, 2009 Re: Specializing on Compile Time Constants  

 
Posted in reply to dsimcha  dsimcha wrote:
> I'm working on a mathematical expression interpreter for D, which would allow
> for closed form mathematical expressions to be specified as string literals at
> runtime and be evaluated. For example:
>
> MathExp myExpression = mathExp("x^2 + e^cos(x)  2 * sqrt(pi)", "x");
> writeln(myExpression(2)); // Does exactly what you think it does.
>
> I've found the syntax so convenient that I'd like to transparently specialize
> it on strings known at compile time. The idea is that, when the expression is
> hardcoded, you will still be able to use the MathExp interface, but your
> expression will evaluate at the full speed of a statically compiled function.
> Is there any way to test whether the value of an argument to a template
> function is known at compile time and specialize on this?
As an aside, I'd so use that if you allowed LaTeX math expressions.
Andrei

October 12, 2009 Re: Specializing on Compile Time Constants  

 
Posted in reply to dsimcha  On 10/12/09 23:55, dsimcha wrote:
> == Quote from Jacob Carlborg (doob@me.com)'s article
>> On 10/12/09 23:49, dsimcha wrote:
>>> I'm working on a mathematical expression interpreter for D, which would allow
>>> for closed form mathematical expressions to be specified as string literals at
>>> runtime and be evaluated. For example:
>>>
>>> MathExp myExpression = mathExp("x^2 + e^cos(x)  2 * sqrt(pi)", "x");
>>> writeln(myExpression(2)); // Does exactly what you think it does.
>>>
>>> I've found the syntax so convenient that I'd like to transparently specialize
>>> it on strings known at compile time. The idea is that, when the expression is
>>> hardcoded, you will still be able to use the MathExp interface, but your
>>> expression will evaluate at the full speed of a statically compiled function.
>>> Is there any way to test whether the value of an argument to a template
>>> function is known at compile time and specialize on this?
>> Doesn't all values to a template have to be known at compile time
>
> No, I mean the *function* parameters of a template function.
Can't you pass the values as template arguments? Seems you working with strings (and numbers?). mathExp!("x^2 + e^cos(x)  2 * sqrt(pi)", "x"); Note the ! after the function name.

October 12, 2009 Re: Specializing on Compile Time Constants  

 
Posted in reply to Jacob Carlborg  == Quote from Jacob Carlborg (doob@me.com)'s article
> On 10/12/09 23:55, dsimcha wrote:
> > == Quote from Jacob Carlborg (doob@me.com)'s article
> >> On 10/12/09 23:49, dsimcha wrote:
> >>> I'm working on a mathematical expression interpreter for D, which would allow for closed form mathematical expressions to be specified as string literals at runtime and be evaluated. For example:
> >>>
> >>> MathExp myExpression = mathExp("x^2 + e^cos(x)  2 * sqrt(pi)", "x");
> >>> writeln(myExpression(2)); // Does exactly what you think it does.
> >>>
> >>> I've found the syntax so convenient that I'd like to transparently specialize
> >>> it on strings known at compile time. The idea is that, when the expression is
> >>> hardcoded, you will still be able to use the MathExp interface, but your
> >>> expression will evaluate at the full speed of a statically compiled function.
> >>> Is there any way to test whether the value of an argument to a template
> >>> function is known at compile time and specialize on this?
> >> Doesn't all values to a template have to be known at compile time
> >
> > No, I mean the *function* parameters of a template function.
> Can't you pass the values as template arguments? Seems you working with
> strings (and numbers?). mathExp!("x^2 + e^cos(x)  2 * sqrt(pi)", "x");
> Note the ! after the function name.
This would work, but it's a bit kludgey because it requires the user to explicitly specify that the string is known at compile time. I was wondering if this could be done transparently.

October 12, 2009 Re: Specializing on Compile Time Constants  

 
Posted in reply to dsimcha  dsimcha: > Is there any way to test whether the value of an argument to a template > function is known at compile time and specialize on this? Do you mean this? http://www.digitalmars.com/webnews/newsgroups.php?art_group=digitalmars.D&article_id=97424 Bye, bearophile 
October 13, 2009 Re: Specializing on Compile Time Constants  

 
Posted in reply to dsimcha  dsimcha wrote:
> == Quote from Jacob Carlborg (doob@me.com)'s article
>> On 10/12/09 23:49, dsimcha wrote:
>>> I'm working on a mathematical expression interpreter for D, which would allow
>>> for closed form mathematical expressions to be specified as string literals at
>>> runtime and be evaluated. For example:
>>>
>>> MathExp myExpression = mathExp("x^2 + e^cos(x)  2 * sqrt(pi)", "x");
>>> writeln(myExpression(2)); // Does exactly what you think it does.
>>>
>>> I've found the syntax so convenient that I'd like to transparently specialize
>>> it on strings known at compile time. The idea is that, when the expression is
>>> hardcoded, you will still be able to use the MathExp interface, but your
>>> expression will evaluate at the full speed of a statically compiled function.
>>> Is there any way to test whether the value of an argument to a template
>>> function is known at compile time and specialize on this?
>> Doesn't all values to a template have to be known at compile time
>
> No, I mean the *function* parameters of a template function.
I may be wrong, but I seem to remember reading somewhere that DMD always tries to evaluate as much as possible at compile time. That is, if a function is CTFEenabled, and its input is known at compile time, it is calculated at compile time.
void main(string[] args) {
auto x = foo(args[1]); // foo() is evaluated at run time
auto y = bar("baz"); // foo() is evaluated at compile time
}
That said, I also seem to remember that the use of structs and classes is very limited (or nonexistent) in CTFE, and I guess your mathExp() is supposed to return a MathExp struct...
Lars

October 13, 2009 Re: Specializing on Compile Time Constants  

 
Posted in reply to dsimcha  dsimcha wrote:
> I'm working on a mathematical expression interpreter for D, which would allow
> for closed form mathematical expressions to be specified as string literals at
> runtime and be evaluated. For example:
>
> MathExp myExpression = mathExp("x^2 + e^cos(x)  2 * sqrt(pi)", "x");
> writeln(myExpression(2)); // Does exactly what you think it does.
>
> I've found the syntax so convenient that I'd like to transparently specialize
> it on strings known at compile time. The idea is that, when the expression is
> hardcoded, you will still be able to use the MathExp interface, but your
> expression will evaluate at the full speed of a statically compiled function.
This is *so* cool. :)
Lars

October 13, 2009 Re: Specializing on Compile Time Constants  

 
Posted in reply to Lars T. Kyllingstad  On 20091013 09:11:08 +0200, "Lars T. Kyllingstad" <public@kyllingen.NOSPAMnet> said:
> I may be wrong, but I seem to remember reading somewhere that DMD always tries to evaluate as much as possible at compile time. That is, if a function is CTFEenabled, and its input is known at compile time, it is calculated at compile time.
>
> void main(string[] args) {
> auto x = foo(args[1]); // foo() is evaluated at run time
> auto y = bar("baz"); // foo() is evaluated at compile time
> }
you are wrong, compile time evaluation is not performed if not requested (by making that constant for example).
The compiler cannot know the complexity of the calculation, and making it at compile time is much slower...
thus you have to explicitly instruct the computer to do it...

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